The pilot stated that with three passengers, he departed from a dock on his property to conduct a local flight. After 1 hour, he returned to the same dock for landing. The approach was normal, but when the pilot came to a 2- to 3-foot hover above the dock the helicopter “dropped violently onto its skids.” The helicopter then began sliding backward with the tail down towards the water. He applied power in an attempt to bring the helicopter to a hover, but then it rolled onto its left side and slid rearward into the water. The rotor, airframe, transmission, engine, and avionics incurred damage. The pilot stated that there were no mechanical abnormalities present with the helicopter prior to the flight, and did not report after the accident experiencing any prior to the initiation of the accident sequence.